Technical Field
The present disclosure relates to a nanocrystalline composite catalyst for storing/supplying hydrogen exhibiting excellent catalytic activity in both a hydrogenation involving a hydrogen-storing body containing an aromatic compound, and a dehydrogenation involving a hydrogen-supplying body containing a hydrogen derivative of the aromatic compound, a nanocrystalline composite catalyst mixture for storing/supplying hydrogen, and a method for supplying hydrogen.
Description of the Related Art
In recent years, hydrogen has attracted attention as a next-generation energy source to replace fossil fuels such as oil. Fuel cell power generation systems using such hydrogen are used as power sources for a diversity of applications to automobiles, consumer power-generation facilities, vending machines, mobile devices, and the like, and technological developments have been rapidly progressing.
However, hydrogen is gaseous at ordinary temperature and normal pressure, and thus is more difficult to store and transport than liquids and solids. Also, hydrogen is a flammable substance, for which care should be taken in handling. Therefore, a major problem is involved in transportation, storage, and supply systems for use of hydrogen.
Recently in particular, as a method for storing hydrogen which is excellent in safety, transportability, and storage capability, an organic hydride system using a hydrocarbon such as cyclohexane or decalin has attracted attention.
For example, although benzene and cyclohexane are cyclic hydrocarbons that have the same carbon atom numbers, benzene is an unsaturated hydrocarbon wherein a carbon-carbon bond contains a double bond, whereas cyclohexane is a saturated hydrocarbon having no double bond. Therefore, cyclohexane is obtained by a hydrogenation involving benzene, and benzene is obtained by a dehydrogenation involving cyclohexane.
By using the hydrogenation and the dehydrogenation involving these hydrocarbons, the storage and supply of hydrogen are enabled. Since aromatic compounds such as benzene are liquid at room temperature, they are excellent in transportability.
Therefore, in recent years, research and development of organic hydride systems using aromatic compounds have been actively performed. For example, a metal support catalyst exhibiting excellent catalytic activity with respect to two kinds of different reversible reactions as the above hydrogenation and the above dehydrogenation, and a system for storing/supplying hydrogen using the metal support catalyst are disclosed in Japanese Laid-Open Patent Publication No. 2001-198469 (JP 2001-198469A). Additionally, in Japanese Laid-Open Patent Publication No. 2007-269522 (JP 2007-269522A), a system for storing/transporting hydrogen using the organic hydride system as described above is disclosed.
In the organic hydride system as described above, it is general to use, as a catalyst, precious metal catalysts exhibiting comparatively excellent catalytic activity, such as platinum (Pt), rhodium (Rh), and palladium (Pd), from the viewpoint of improving reaction efficiency. However, since the precious metal catalyst such as platinum is expensive, and has a resource depletion problem, reduction in the amount of the precious metal catalyst to be used is required in recent years. However, the reduction in the amount of the precious metal catalyst to be used is not considered at all in both JP 2001-198469A and JP 2007-269522A.
As means for reducing the amount of the precious metal catalyst to be used, for example, by making catalyst particles finer to nanoparticles having a nanometer scale particle diameter of less than 1 μm, it is useful to increase the area (surface area) ratio of a catalyst surface (active surface) producing a catalyst reaction, or to substitute an inexpensive transition metal or oxide thereof for a part of the precious metal catalyst.
However, when making the catalyst particles finer to the nanoparticles, a problem is that the aggregation and the like of the finer catalyst particles prevent the increased active surface from being effectively utilized. When substituting the transition metal or oxide catalyst thereof, a problem is that these catalysts have lower catalytic activity than the precious metal catalyst has.
Therefore, even if the amount of the precious metal catalyst to be used is reduced using these means, the reaction efficiency of the above reaction also tends to decrease with the reduction in the amount of the precious metal catalyst to be used, so that the sufficient reduction in the amount of the precious metal catalyst to be used has not yet been achieved.